Starwatch March 2013

February 12, 2013

Image of the red supergiant star Betelgeuse, in Orion, by the European Southern Observatory's Very Large Telescope. The resolution is equivalent to seeing a tennis ball on the International Space Station from the ground. Credit: ESO and P. Kervella

By Deane Morrison

Once again, astronomers wait with bated breath to see if a new comet will turn out to be a delight or a dud.

Comet Pan-STARRS reaches maximum brightness around the 9th-10th, but it may be easiest to find on the 12th, when a thin crescent moon can help. Look west about 45 minutes after sunset, using binoculars if necessary; the comet will be about four degrees, or eight full moon widths, left of the moon. Pan-STARRS moves northward each successive night, appearing below and slightly right of the moon on the 13th. It will quickly fade, so try to catch it if you can.

Saturn, a morning planet, begins the month by rising in the east around 11 p.m. It comes up two hours earlier by month's end, but with the onset of Daylight Time, that translates to 10 p.m. The bright star just to the west of Saturn is Spica, representing an ear of grain held by Virgo, the virgin. Saturn's rings are nearly 19 degrees from horizontal, and it brightens steadily as Earth prepares to lap it in the orbital race.

While Earth is gaining on Saturn, it's busy leaving Jupiter in the dust. Jupiter comes out blazing in the west-southwest, still hugging Taurus and its brightest star, Aldebaran. Try looking on the 17th, when a fat, waxing lunar crescent hangs below the giant planet. Jupiter is now moving eastward through Taurus, but Earth's orbital motion is carrying the whole assemblage westward, into the sun's afterglow.

The full moon comes the morning of the 27th at 4:27 a.m. CDT. This moon was known to various Algonquin tribes as the full worm moon, for the reappearance of earthworms; the full crow moon, for their late-winter cawing; the full crust moon, for the icy crust on snow that has thawed and refrozen; or the full sap moon, as the time of maple sugaring is now nigh.

Spring arrives with the equinox at 6:02 a.m. CDT on the 20th. Since the fall equinox, sunrises have been later and sunsets earlier the farther north you went. But at the spring equinox, all that reverses. Now, the farther north you go, the longer the day. And at the exact moment of the equinox—either one—an observer from space would see the sunrise or sunset line cutting the Earth in half vertically, from pole to pole.

The Andromeda Galaxy, the Milky Way's closest large neighbor, made news recently because of the tiny dwarf galaxies that orbit it. There are dozens known, and they have been thought to be remnants of primordial structures that helped form big galaxies like the Milky Way. It was also thought that they orbited each in its own orbit, sort of like bees swarming around a hive, or that they formed along an extensive filament of material that is falling into a galaxy.

Now a team of astronomers has found that 13—almost half—of Andromeda's known dwarf galaxies orbit in a single plane that is sharply tilted with respect to Andromeda's plane and about a million light-years in diameter, which makes it close to 10 times as broad as our galaxy. There has been debate about whether some of the Milky Way's dwarf companions also form a similar structure, so this discovery is sure to influence further research and theories about how all galaxies formed.

The University of Minnesota offers public viewings of the night sky at its Duluth and Twin Cities campuses. For more information and viewing schedules, see: